Hundreds of California protesters shut down freeways and marched in the state capital after police fatally shot an unarmed black father in his grandparents’ backyard, firing 20 rounds into the 22-year-old who was carrying only a cellphone.

Sacramento demonstrators shouting “Shut it down” disrupted rush-hour traffic on Thursday night and blocked thousands of NBA fans from entering the Sacramento Kings arena to protest against the killing of Stephon Clark, who was shot in his family’s home on Sunday after police wrongly assumed he was armed with a gun.

The protests erupted as body-camera and helicopter videos of officers firing bullets into Clark went viral, with his death sparking comparisons to other high-profile cases of US police killing unarmed black people, including Tamir Rice, Walter Scott and Oscar Grant.

A child holds up a picture of Stephon Clark during a protest. Photograph: John G. Mabanglo/EPA

The Sacramento police department said officers were responding to reports of a man breaking into vehicles, but Clark’s relatives told reporters he was probably trying to enter the house through the garage since the house’s front doorbell was broken.

On the video, one of the officers is heard yelling, “Gun, gun, gun”. Police officials initially told local media that Clark was found with a “tool bar” on him, but later clarified that he was only holding a phone.

On Thursday, the game between the Kings and Atlanta Hawks was played before about 2,000 fans in the 17,000-seat arena. The protesters eventually dispersed, and no arrests were made.

After the game, the Kings owner, Vivek Ranadivé, addressed the small crowd from center court, surrounded by Sacramento’s players and coaches, and expressed sympathy for Clark’s family.

“We are so very sorry for your loss,” Ranadive said. “We at the Kings recognize people’s abilities to protest peacefully and we respect that. We here at the Kings realize that we have a big platform. It’s a privilege but it’s also a responsibility. It’s a responsibility that we take very seriously and we stand here before you, old, young, black, white, brown, and we are all united in our commitment.”

“We are at a place of deep pain” because of recent violence directed at black people in Sacramento and elsewhere, said the Rev Les Simmons, a community leader who joined the protest.

Clinton Primm, who was friends with Clark, a father of two sons ages one and three, said: “He was a great dad. He loved both of them to death.”

A California officer urges protesters to move off an interstate highway during the Thursday demonstration. Photograph: Sacramento Bee/TNS/Sipa USA/REX/Shutterstock

Independent experts said the footage from body cameras and the police helicopter raised more questions than they answer.

Geoffrey Alpert, a professor of criminology at the University of South Carolina and an expert on police use of force, said the officers may have a tough time explaining why they jumped to the conclusion that Clark had a gun.

He also questioned why an arriving backup officer had the two original officers turn off the microphones on their body cameras, eliminating what he called “important evidence”.

In an ideal world, the two officers should have immediately provided first aid instead of waiting five minutes for backup, added Eugene O’Donnell, a professor of police studies at John Jay College of Criminal Justice.

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Salena Manni, Clark’s girlfriend and the mother of his children, told the Sacramento Bee earlier in the week that the family was struggling to process the tragedy.

Stevante Clark described his brother Stephon as an outgoing person who was dedicated to his children, in a local television interview: “He was a people person who everybody wanted to be around. We came from underprivileged, broken homes, but he didn’t care about nothing else but his kids.”